Once again The Trident!

[terry michaels]

Message text written by Haible Juergen
> 
        >The Moog oscillators that used a common expo converter for
multiple
        >oscillators, was that voltage or current?

Current.<

Hi Juergen:

Sorry to differ on this, but the 901A drove multiple 901B's with a variable
voltage.  The op amp driving the diode string in the expo converter had an
output stage consisting of a PNP transistor with a resistor from the
emitter to +12V, the base voltage of the transistor was brought out to the
edge connector on the PCB, from there it went to typically three 901B's. 
Each 901B had a PNP transistor matched to the one in the 901A, with a
resistor from the emitter to +12V, the transistors were all matched, so the
same current (and hopefully the same frequency) should be delivered by each
one.  This arrangement was part of the reason the 901 series VCO's drifted
so much, the transistors were on separate circuit cards in separate
modules, temperature differences between the transistors would alter the
forward bias of each one, and though there was resistive emitter
degeneration, it would still create some degree of linear frequency offset.

The input op amp used a normal resistor instead of a +3500ppm tempco, so
the scale factor drifted also.

Terry Michaels